Optical metrology is commonly employed in process control applications in the semiconductor manufacturing industry due to optical metrology's non-contact and non-destructive nature. Two commonly used optical metrology techniques are reflectometry and ellipsometry.
In optical metrology, a sample is illuminated with broadband or single wavelength light and the light is detected and analyzed after it interacts with the sample. FIG. 1 illustrates a side view of a sample 10 with a grating 12 that is being illuminated with a probe beam 14 having a normal angle of incidence and a probe beam 16 having an oblique angle of incidence. Typically, but not always, the oblique angle of incidence probe beam 16 is used with an ellipsometer and the normal incidence probe beam 14 is used with a reflectometer. The probe beams 14 and 16 are illustrated as reflected from the grating 12 (which in the case of a diffraction grating is the zeroth order diffracted light) as beams 15 and 17, respectively. The normal incidence probe beam 14 and the reflected beam 15 are illustrated as laterally displaced, but it should be understood that these beams coincide due to their normal orientation.
As semiconductor geometries continue to shrink, increasing demands are placed on the optical metrology techniques. Moreover, the use of non-planar structures, such as FinFET devices, Intel's tri-gate and AMD's multigate device, provides additional challenges to optical metrology, as three-dimensional structural information is difficult to extract.
Accordingly, improved optical metrology devices and methods are desired.